The present invention relates to the use of certain fumaric acid monoalkyl esters either in the form of salts thereof or as the free acid, alone or in combination with a dialkyl fumarate, for preparing pharmaceutical compositions for use in transplantation medicine. In particular, it relates to the use of said pharmaceutical preparations containing fumaric acid alkyl esters for treating, alleviating or suppressing rejection of the transplant by the recipient, i.e. host-versus-graft reaction.
Transplantations are tissue or organ transplantations, i.e. the transfer of tissue such as cornea, skin, bones (bone chips), vessels or fasciae, of organs such as kidney, heart, liver, lung, pancreas or intestine, or of individual cells such as islet cells, xcex1-cells and liver cells, the kidney having the greatest significance as a transplanted organ.
According to the degree of relationship between the donor and the recipient we differentiate between auto-transplantation (transfer to another part of the body of the same individual), iso-transplantation (transfer to another, genetically identical individual) or allogenic transplantation (transfer to another individual of the same species). Depending on the site of origin and transplantation, we further differentiate between homotopic transplantation (transfer to the same site) and heterotopic transplantation (transfer to a different site). The above-mentioned transplantations play an important role in modern medicine.
A major problem in transplantation medicine is graft rejection after transplantation of the tissue, organ or cell by immunological defence reactions of the recipient. Such a graft rejection is also called host-versus-graft reaction. The immunological defence reaction of the organism against the heteroprotein often results in rejection or dissolution of the grafts. By using modern immunosuppressive agents, the most important representatives of which are the cyclosporines, especially cyclosporine A, a significant improvement in the results of transplantations was achieved over the last few years. At present, the one-year survival rate is about 60% for liver transplantations, about 80% for heart transplantations and over 90% for kidney transplantations.
In host-versus-graft reactions, different stages may be distinguished. Depending on the degree of difference between the recipient and the donor, this reaction takes place at different speeds so that we speak of a an acute, sub-acute or chronic reaction. Acute rejection processes are accompanied by the irreversible loss of the transplant (necrotisation) as a result of arteriitis or arteriolitis within 48 hours and cannot be influenced by the administration of drugs. The subacute rejection reaction becomes manifest as a rejection crisis from day 12 to month 4 with reversible functional disorders as a result of a transplant vasculopathy. Finally, the loss of function of the transplant as a result of vascular changes such as obliterating arteriopathy, which proceeds over weeks or years and can practically not be influenced by drugs, is termed a chronic rejection reaction.
To avoid such rejection reactions, i.e. the host-versus-graft reaction, transplantation medicine essentially makes use of immunosuppression, i.e. a weakening of the normal immunoresponse. For this purpose, anti-lymphocyte sera are often used in combination with corticosteroids and so-called anti-metabolites, e.g. purine analogues such as 6-mercaptopurine and thioguanine which affect the nucleic acid and protein synthesis and thus prevent cell division and proliferation. This leads to suppression of the production of antibodies and the cellular immune response. The immunosuppressive agents used for therapy are substances which suppress or weaken the immunoreaction in the body either specifically or non-specifically. Non-specific immunosuppressive agents are cytostatic agents such as, for example, alkylating agents or antimetabolites. In addition, active ingredients are known which cause at least partial specific immunosuppression, such as corticosteroids, antisera, antibodies FK-506, tacrolimus, mycophenolatemofetil and primarily cyclosporines such as cyclosporine A.
The danger in using immunosuppressive agents lies in weakening the body""s defence against infectious diseases and the increased risk of malignant diseases. Therefore, it is the object of the invention to provide a pharmaceutical preparation to be employed in transplantation medicine which may be used to treat, especially to suppress, weaken and/or alleviate host-versus-graft reactions but does not have the above disadvantage.
The object of the invention is achieved by using certain fumaric acid monoalkyl esters as salts with mono- or bivalent cations or in the form of the free acid, either alone or in combination with a dialkyl fumarate for preparing pharmaceutical compositions to be used in transplantation medicine. The subject matter of the invention is characterised in detail in the claims. The compositions according to the invention do not contain free fumaric acid per se.
It is known that pharmaceutical preparations which, upon biological degradation after administration, enter into the citric acid cycle or are part thereof gain increasing therapeutic significancexe2x80x94especially when given in high dosagesxe2x80x94since they can alleviate or heal diseases caused cryptogenetically.
Fumaric acid, for example, inhibits the growth of the Ehrlich ascites tumour in mice, reduces the toxic effects of mitomycin C and aflatoxin [K. Kuroda, M. Akao, Biochem. Pharmacol. 29, 2839-2844 (1980)/Gann. 72, 777-782 (1981)/Cancer Res. 36, 1900-1903, (1976)] and displays a anti-psoriatic and anti-microbial activity [C. N. Huhtsnen, J. Food Sci. 48, 1574 (1983)/M. N. Islam, U.S. Pat. No. 4,346,118 dated Aug. 24, 1982/C.A. 97, 161317b (1982)].
When administered parenterally, transdermally and especially perorally, high dosages of fumaric acids or its derivatives known so far such as dihydroxyl fumaric acid, fumaramide and fumaronitrile have such unacceptably severe side effects and high toxicity [P. Holland, R. G. White, Brit. Dermatol. 85, 259-263 (1971)/M. Hagedorn, K. W. Kalkoff, G. Kiefer, D. Baron. J. Hug, J. Petres, Arch. Derm. Res. 254, 67-73 (1975)] that, in most cases, such a therapy had to be abandoned in the past.
European Patent Application 0 188 749 already describes fumaric acid derivatives and pharmaceutical compositions containing the same for the treatment of psoriasis. Pharmaceutical compositions for the treatment of psoriasis containing a mixture of fumaric acid and other fumaric acid derivatives are known from DE-A-25 30 372. The content of free fumaric acid is obligatory for these medicaments.
DE-A-26 21 214 describes medicaments containing the fumaric acid monoethyl ester and its mineral salts as active ingredient for the treatment of psoriasis. The publication xe2x80x9cHautarzt (Dermatologist) (1987) 279-285xe2x80x9d discusses the use of fumaric acid monoethyl ester salts. Pharmaceutical compositions containing a mixture of fumaric acid monoalkyl ester salts and a fumaric acid diester for the treatment of psoriasis, psoriatic arthritis, neurodermatitis and enteritis regionalis Crohn are known from EP 0 312 697 B1.
Surprisingly, it has now been found that fumaric acid-C1-C5-monoalkylester(s) in the form of a salt thereof with mono- or bivalent cations, preferably in the form of calcium, magnesium, zinc or iron salts or lithium, sodium or potassium salts, or in the form of free acid, either alone or in combination with a di-C1-C5-alkyl-fumarate are advantageous for preparing a pharmaceu-tical composition for use in transplantation medicine. Compositions containing such fumaric acid C1-5-monoalkyl esters surprisingly permit a positive modulation of the immune system in host-versus-graft reactions.
The invention preferably uses pharmaceutical compositions containing one or more compounds from the group consisting of calcium, magnesium, zinc and iron salts or lithium, sodium or potassium salts of fumaric acid monoalkyl esters of the general formula 
optionally in admixture with dialkyl fumarate of the formula 
optionally together with customary pharmaceutical excipients and vehicles,
wherein A is a bivalent cation from the series consisting of Ca, Mg, Zn or Fe or a monovalent cation from the series Li, Na or K, respectively, and n denotes the numeral 1 or 2 depending on the type of cation.
Pharmaceutical compositions containing one or more alkyl hydrogen fumarates of the general formula 
optionally in admixture with dialkyl fumarate of the formula 
and, optionally, commonly used pharmaceutical excipients and vehicles, may also be used to advantage.
The use where the active ingredients are administered perorally in the form of tablets, micro-tablets, pellets or granulates in capsules or (soft or hard gelatine) capsules is preferred.
Preferred compositions according to the invention contain the calcium salt of the fumaric acid monomethyl ester or monoethyl ester or the calcium salt of the fumaric acid monomethyl ester or monoethyl ester in admixture with dimethyl fumarate.
Preparations containing the calcium salt of the fumaric acid monoalkyl ester or the fumaric acid alkyl ester in the form of the free acid in an amount of 10 to 300 mg are especially suitable for administration, the total weight of the active ingredients being 10 to 300 mg.
Other preferred oral forms of administration contain 10 to 290 parts by weight of the calcium salt of the fumaric acid monoalkyl ester and 290 to 10 parts by weight of dimethyl fumarate as well as 1 to 50 parts by weight of the zinc salt of the fumaric acid monoalkyl ester or 1 to 250 parts by weight of dimethyl fumarate, 1 to 50 parts by weight of the magnesium salt of the fumaric acid monoalkyl ester, for example monomethyl ester, the total weight of the active ingredients being 30 to 300 mg.
Preferred compositions according to the invention also contain the methyl hydrogen fumarate in an amount of 10 to 300 mg.
It is also possible to use the drugs in the form of compositions for percutaneous and transdermal administration and compositions for rectal administration.
The fumaric acid derivatives contained in the compositions according to the invention, are, for example obtained by
a) condensation of a compound of the formula 
xe2x80x83with 2 moles of dialkyl alcohol (ROH) by a known method to obtain a diester, followed by controlled hydrolysation to obtain a monoester, or
b) condensation with 1 mole of the relevant alkyl alcohol in the usual manner followed by hydrolysis of the monoacid chloride thus obtained to obtain an acid, or
c) direct condensation of the fumaric acid with 2 moles of alkyl alcohol (ROH) by a known method to obtain the relevant diester followed by controlled hydrolysation to obtain the monoester, or
d) direct condensation of maleic acid or maleic anhydride with 1-2 moles of the relevant alkyl alcohol (ROH) by a known method to obtain a mono- or diester followed by catalytic isomerisation to obtain the respective fumaric acid derivative.
The salts of the fumaric acid monoalkyl esters may also be obtained by reacting a compound of the general formula 
wherein R is a C1-C5 alkyl group with equivalent mole amounts of Na, K, Fe, Ca, Mg or Zn hydroxide or oxide in toluene and removing the water generated during the reaction.
For particularly preferred applications, compositions containing the following active ingredients in the stated dosages and proportions are used:
1) a pharmaceutical composition for peroral administration in the form of tablets, micro-tablets or pellets in capsules or capsules, characterised in that it contains the calcium salt of the fumaric acid monomethyl ester in an amount of 10 to 300 mg, the total weight of the active ingredients being 10 to 300 mg;
2) a pharmaceutical composition for peroral administration in the form of tablets, micro-tablets or pellets in capsules or capsules, characterised in that it contains 10 to 290 parts by weight of the calcium salt of the fumaric acid monomethyl ester and 290 to 10 parts by weight of dimethyl fumarate, the total weight of the active ingredients being 20 to 300 mg,
3) a pharmaceutical composition for peroral administration in the form of tablets, micro-tablets or pellets in capsules or capsules, characterised in that it contains 10 to 250 parts by weight of the calcium salt of the fumaric acid monomethyl ester, 1 to 50 parts by weight of dimethyl fumarate and 1 to 50 parts by weight of the zinc salt of the fumaric acid monomethyl ester, the total weight of the active ingredients being 20 to 300 mg,
4) a pharmaceutical composition for peroral administration in the form of tablets or capsules, characterised in that it contains 10 to 250 parts by weight of the calcium salt of the fumaric acid monomethyl ester, 250 to 10 parts of dimethyl fumarate, 1 to 50 parts by weight of the magnesium salt of the fumaric acid monomethyl ester and 1 to 50 parts by weight of the zinc salt of the fumaric acid monomethyl ester, the total weight of the active ingredients being 30 to 300 mg.
The following drug forms, dosages and proportions are also preferred:
5) a pharmaceutical composition for peroral administration, characterised in that it contains one or more compounds from the group of free acids of fumaric acid monoalkyl esters of the general formula 
xe2x80x83optionally in admixture with dialkyl fumarate of the formula 
xe2x80x83and vehicles, said compositions not containing fumaric acid in its free form;
6) a pharmaceutical composition for oral administration in the form of tablets, micro-tablets or pellets in capsules or capsules, characterised in that they contain alkyl hydrogen fumarate, preferably methyl hydrogen fumarate, in an amount of 10 to 30 mg, the total weight of the active ingredients being 10 to 300 mg.
7) a pharmaceutical composition for oral administration in the form of tablets, micro-tablets or pellets in capsules or capsules, characterised in that they contain 10 to 290 parts by weight of alkyl hydrogen fumarate, preferably methyl hydrogen fumarate, and 290 to 10 parts by weight of dialkyl fumarate, the total weight of the active ingredients being 20 to 300 mg.
Oral compositions may be covered by an enteric coating. Said compositions may be provided in the form of microtablets, pellets or granulates which may be contained in capsules. Such capsules may be soft or hard gelatine capsules.
According to a preferred embodiment, the size or the average diameter of the pellets or micro-tablets is in the range of 300 to 2000 xcexcm, especially in the range of 500 or 1000 xcexcm.
According to the invention the therapy with fumaric acid monoalkyl esters or salts thereof may also be carried out in combination with one or more compositions of the triple drug therapy commonly used in organ transplantations or with cyclosporine A, especially for the treatment, alleviation or suppression of host-versus-graft reactions.
For this purpose, the compositions administered may contain a combination of the active ingredients in known dosages or amounts. Likewise, a combination therapy may consist of the parallel administration of separate compositions by the same or a different route of application. Optionally, the dosage of the active ingredient contained in addition to the fumaric acid derivative dosage administered in accordance with the invention may be reduced with advantageous results.
Another embodiment of the use according to the invention is to alternate the drug therapy with immunosuppressive agents such as cyclosporine in sequence with an application of the above-mentioned fumaric acid derivatives. This means that an application of fumaric acid derivatives as defined above over one or more weeks may follow a cyclosporine therapy of one or more weeks. This permits reduction of the Cyclosporine A dosage resulting in a considerable decrease of the rate of side effects in long-term therapy.